February 27, 2018

RC Coordinators Join Forces with Student Volunteers to Assess Hurricane Impact on Caribbean Reefs

In Dominica, a large area of fragile branching corals was flattened by hurricane waves

Photos by Brittany Holbrook

In late January, a team of scientists led by Reef Check Executive Director Dr. Gregor Hodgson surveyed the reefs of Nevis and Dominica to determine the effects of Hurricanes Irma and Maria on the Caribbean islands. Dr. Hodgson joined forces with long-time Reef Check Caribbean Coordinators Jim Hewlett and Arun “Izzy” Madisetti and a group of four student volunteers- Brittany Holbrook, Brooke Day, Marissa Hassevoort, and Morgan Anderson. Vaughn Sturge, a dive master and EcoDiver from Nevis, also participated. The trip was the first phase of their investigation to find out exactly what happened underwater last September. The work was funded by the Geneva based Oak Foundation and US National Science Foundation.

From the air, the formerly lush tropical forests of Dominica looked like matchsticks spilled from a box. On the ground, the team drove past miles of collapsed telephone poles, destroyed homes and blue tarps covering damaged roofs. The team was nervous about what they'd find below the surface—could the coral reefs survive the high winds, huge waves and flooding that decimated hotels and killed more than 30 people?

After seeing the terrible damage on land, the team expected to see similar destruction underwater. While they did find some reefs formerly comprised of fragile branching coral species had been flattened, they were pleasantly surprised to discover that most of the reefs surveyed only suffered moderate damage, with about 15% of the corals broken or killed. After 10 days of surveys, the team concluded that the major threats to the health of reefs in Nevis and Dominica are overfishing and rising seawater temperatures.

“Coral reefs are the most sensitive ecosystem in the world to global warming. They're being destabilized by over-fishing and killed off by climate change,” Hodgson said. “It's a mystery to piece together what happened after these two massive hurricanes swept over reefs that aren't being monitored often.”

The team spent every day carrying out surveys using two main techniques. The first, called the “manta tow”, is a slow motion sled ride. The observer clings on to a flat board stopping every few minutes to record the level of damage among other parameters and the coordinates.

At certain points, they stopped to deploy a team of divers to do a more detailed Reef Check survey involving counting fish, shellfish and other invertebrates, and finally the corals that provide the foundation for the ecosystem, recording the counts on waterproof paper.

In the face of some difficult and dangerous situations, the team proved they were up to the task. One day Marissa was stalked by a barracuda and had to “walk on water” to get back to the boat, and on another day, the boat engine broke, producing spectacular black clouds of diesel smoke. In exposed coastal areas waves were often 10 feet high making it difficult to tow a diver. During lunch breaks the boat crew taught the students how to fillet the invasive lionfish to make ceviche.

After completing the surveys, Hodgson wrote up a summary report to help the World Bank and the Fisheries Department of Dominica to determine what funding would be needed to restore the damaged reefs. After returning to Los Angeles, Hodgson began the process of analyzing the results in more detail with the help of the field team and other scientists.

The results showed that in a few areas, the hurricanes wiped out patches of fragile finger corals, sea fans, large barrel sponges and gorgonians, leaving rubble and dead corals scattered on the sea floor. However, most areas only suffered minimal damage, likely due to the mound-shaped corals being adapted to wave action over time.

In fact, not all the changes were bad – the hurricanes ripped out a lot of algae that had been overgrowing and killing the corals. In the short term, this will open up space allowing coral larvae to settle and grow back.

“The hurricane damage wasn't as bad as we all expected, but the goal of Reef Check is to assess all human impacts,” Hodgson said. “I was surprised how few fish were counted and how small they were in both Nevis and Dominica.”

Fishing down the food chain results in algae-eating fish like doctorfish getting fished out. Without these herbivores, some reefs had already been converted from coral reefs to sponge and algae reefs.

“It's very sad,” Hodgson said. “Between coral bleaching and overfishing, we've lost a dramatic amount of reefs in the past four years all over the world. We need to wake up soon or we won't have reefs.”

This brain coral was broken and rolled by the hurricane, now mostly dead, but a small tan piece is still alive and will likely recover.

Global warming caused the Caribbean to heat up 1 or 2 degrees F during the last El Niño (2014-16). While a 1 degree F rise in temperature is nothing for most animals, corals are super sensitive so they “bleach,” then many die. Luckily, the reefs in Dominica and Nevis have not yet been affected much by bleaching.

Hurricanes also derive their destructive energy from the heat of ocean water. The hotter the water, the higher the possible wind speeds. Wind speeds in Dominica reached 180 mph – enough to pick up a car and toss it like a toy. The stronger the wind, the bigger the waves—and it is the wave energy that can rip up a coral reef.

Coral reefs are the most at-risk ecosystem in the world. Unless the world can get a handle on global warming, increasingly more powerful hurricanes will cross the Caribbean killing more coral, and higher water temperatures will increase the chances of coral bleaching and death. The loss of coral reefs will reduce the amount of fish and coastal protection, damage the tourism industry, and potentially limit the number of future pharmaceutical discoveries of “drugs from the sea. “
“We see the pattern with the warming ocean,” Hodgson said. “Yet one billion people depend on food from coral reefs.”

But it's not too late. If the damaging conditions are reversed, the reefs and fish will come back in as little as five years.

Hodgson believes solutions include restricting fishing through the creation of marine protected areas, developing sustainable aquaculture on the islands to grow more fish for local consumption and exporting fish and algae to sell to other countries.

Reef Check aims to educate and empower the public to care more about the ecosystem by training volunteer divers.

“We train divers because we want them to care about the ocean. You care about what you know,” Hodgson said. “You go in the ocean, you see it, you love it. You can't love what you don't know.”


Thousands of trees were knocked down and some were swept out onto the reefs in Dominica

Large mound coral and branching corals were dislodged and broken up by the hurricanes.

Some branching corals on this reef were damaged and others survived.


Rubble, algae, sand and broken tree branches were deposited on the reefs during the storms.

Many sea whips were broken off by storm waves and added to the broken hard coral branches on the seabed.

Professor Jim Hewlett reels in the transect line used to measure the damage to the reef. Many reefs like this one are covered in algae due to the lack of herbivorous fish and invertebrates to “mow the lawn.”